1. Field of Invention
The invention relates to managing traffic in data communication systems in which dissimilar CDMA (code division multiple access) channels are present. More particularly, the invention relates to managing traffic in data communications systems in which a lower-capacity, “random access” (reservationless) asynchronous CDMA channel is present alongside a higher-capacity, “reservation-oriented” orthogonal CDMA channel.
2. Related Art
In Time Division Multiple Access (TDMA) based systems, available bandwidth is divided into time slots. The time slots are further divided into two general categories: Random Access Time Slots (RATS), and REservation Time Slots (RETS).
RATS are assigned as contention time slots where different customer premises equipments (CPEs) contend for resources. ALOHA-based contention resolution protocols are typically used on the RATS to resolve collision among customer premise equipments (CPEs). CPEs send a small packet on the RATS to request bandwidth on the RETS. Depending on the system, small packets may be transmitted on the RATS, but most traffic is sent over the RETS by first requesting for bandwidth.
TDMA systems suffer from two main disadvantages: longer access delay and lower bandwidth efficiency. Because a request needs to be sent on the RATS prior to acquiring reservation, a long delay is introduced. RATS time slots need to be operated at very low traffic loading to avoid excessive collisions and delay. This results in the lower bandwidth efficiency of TDMA systems.
Accordingly, there is a need in the art for a technique that provides shorter access delay and higher bandwidth efficiency. To this end, code division multiple access (CDMA) has been adopted. It has been generally recognized (Bhargava et al., Digital Communications by Satellite, John Wiley & Sons, New York, 1981, see esp. Chapter 9) that CDMA allows users to operate at a same nominal frequency while requiring minimal frequency or time coordination among users.
Different approaches to implementing CDMA have arisen. That is, CDMA channels that are dissimilar in some respects, such as asynchronous code division multiple access (ACDMA, see TIA/EIA/IS95 standard) and orthogonal code division multiple access (OCDMA), have allowed flexibility in designing communications systems. However, with the ability to incorporate multiple dissimilar channel types into a single communications system comes a requirement to effectively manage traffic on the dissimilar channels. For example, there is a need to optimize use of the dissimilar channels, in order to maximize overall system throughput while fairly allocating bandwidth among contentious terminals. However, the complexity of the dissimilar CDMA approaches has made optimum traffic management difficult.
Accordingly, there is a need in the art to provide an arrangement for effectively managing traffic on communications networks with different channels, especially dissimilar CDMA channels.